Depending on the starting components, reaction mixtures of the type to which this invention is directed form solid, microporous materials or foams, particularly, for example, polyurethane foams. In spite of the high standards which have been attained, the production of perfect moldings, for which a homogeneous mixing of the reaction components is a prerequisite, from such reaction mixtures in molds constantly imposes new demands on machine technology and production engineering.
To meet the requirements which have been imposed, high pressure mixing heads with counterflow injections and optional cleaning pistons have won recognition (U.S. Pat. No. 3,263,928). Since these mixing heads have to produce relatively small quantities of mixture to fill the cavity of a typical mold and require a high throughput per time unit in the continuous mixing process, deficiencies have resulted in thoroughness of the mixing, however. Disadvantages caused by the intrusion of air due to the turbulent flow during introduction of the mixture into the cavity of molds have been observed. Attempts have been made to overcome these disadvantages through the use of after-mixers connected downstream of the actual mixing chamber, or choke points which are to ensure a corresponding after-mixing and, in conjunction with a long outflow channel, to ensure a laminar flow upon entry of the components into the mold cavity (U.S. Pat. Nos. 3,924,989; 3,975,128 and 4,141,470).
Although these further developments presently meet the requirements which have been made, they are so expensive and, because of the additional apparatus involved, susceptible to failure, that simplified solutions are being sought.
An object of the present invention is to provide a process in which the mixing operation takes place in a single zone at a high intensity and in which the flow of reaction mixture leaving the mixing zone has already attained a high level of stabilization. Moreover, a mixing head is provided which ensures the necessary mixing intensity of components as well as that the outflow from the mixing chamber is as homogeneous as possible, and that the chamber is also to be self-cleaning in a known manner.